A teletypewriter (hereinafter referred to as a TTY) has been developed and is used to aid communications by a person who has a difficulty, for example, in speech and/or hearing (hereinafter referred to as a TTY holder). Such a TTY holder can communicate with others in remote places by using the TTY. The TTY is usually connected to a telephone and in response to TTY holder's typing texts in the TTY, character signals based on the typed texts are transmitted through the telephone.
In recent years, radio communication apparatuses have been popularized. The radio communication apparatuses are, for example, used in a radio communication system or a mobile radio communication system, such as a portable telephone system or an automobile telephone system. Further, some or many types of the radio communication apparatuses are nowadays featured to be connectable to the TTY so as to allow the TTY holder to use the TTY outside the house through a radio communication apparatus. The TTY is, however, quite large in size and is usually cumbersome for the TTY holder to carry outside.